It is possible to manufacture formed sheet metal posts and beams that can be used as an alternative building material to wooden studs, rafters, stringers, and beams that have been commonly used. It is advantageous to produce such structural members in a manner that may tend to enhance their strength-to-weight ratio, while also tending to reduce the heat loss that may occur across the section of the structural member. As shown in U.S. Pat. No. 5,527,625 of Bodnar, issued Jun. 18, 1996, one way to address these objective is to provide a roll-formed metal member having a web and a pair of opposed flanges, in a generally C-shaped channel-like section, and then to blank the web to leave alternating diagonal struts with formed flanges such that the remaining web has a somewhat truss-like appearance when viewed perpendicular to the web.
The manner in which the openings are formed through the web of the structural member, and the manner of forming the flanges, is such that it is advantageous to provide a relatively smoothly radiused transition into the web adjacent to the opposed out-of-plane flanges.
In a conventional wooden stud or rafter, services, such as electrical power wiring, plumbing, telephone or other communications wiring, or built-in vacuum lines, may tend to be carried though holes bored in the mid-section of the stud or rafter. Wooden studs tend not to be good electrical conductors, and may tend to dampen vibration. In most cases services can be mounted directly in contact with the wood. It is not desirable to have holes bored in sheet metal structural members on the job site, since this is a process over which there is very little quality control, and hence significant opportunity to impair the structural performance of the section. Furthermore, in a formed sheet metal structural member that has had openings blanked in it, and flanged struts formed in it adjacent to the openings, there may be little or no need to drill additional openings.
However, while it would be possible to run services directly through the openings formed in the web, it may also be undesirable. The formed metal member may have sharp edges, and it may tend not to be practical to have all of those edges smoothed down. It may not be desirable to have electrical wiring chafe against a sharp metal edge over a period of time, under vibration loads. Similarly, it may not be desirable to run water pipes, whether hot or cold, in direct contact with the metal section. For these reasons an intermediate isolating or cushioning member may be desired.
A cushioning member, or grommet, for use with the formed sheet metal structural member has a number of desirable properties. In a construction project such a grommet may be required at one or more formed openings in every stud in a wall, and in one or more walls in every room in a house or other building. The person installing the grommets may do so many times per day. An installation that requires complicated tools or procedures is unlikely to be one that will be undertaken with a high level of diligence on a repetitive basis, particularly as the installer grows weary or disinterested.
While it is advantageous for the grommet to be easily installed, it is also desirable that the grommet not tend to be too easily removed. The grommet may be required to stay in service for many years. A loose fit may not be desirable, particularly if vibration is a concern, as it may be in a water pipe fitting, or a fitting subject to repetitive loading over a relatively long period of time.
In the type of sheet metal structural member in question, the depth of the strut flanges may tend to be greatest at mid strut, and may tend to be reduced in the radiused corners where the struts meld into the margin of the web that adjoins the flanges. The dimensional control over the distance from strut to strut may tend to be poorest at mid strut, and relatively greater in the corners of the opening adjacent to the web margin. The web margin may also tend to be a region of lesser potential for deflection due to vibration than the mid strut region. It is advantageous to have an insulating grommet that is capable of engaging the root corners of the formed opening.
It is advantageous to produce a family of grommets of the same, or similar, base width dimension, each having a different attitude for use with a different width of structural member, rather than using the same longitudinal base to cross-web altitude aspect ratio. The use of the same aspect ratio grommet at different sizes would correspond to structural members having greater pitch centers between adjacent openings. When using a rotary press with interchangeable dies, the pitch center distance is determined by the fixed radius of the successive pivot axes of the rotary dies carriers and seats. Since it is difficult to change this dimension it is advantageous to change the height of the openings transverse to the web, while maintaining the pitch between openings at a constant distance.